Some fossil fueled power plants combust coal for the production of steam and electricity. Coal contains sulfur. As a result of the combustion of the coal, a portion of the sulfur reacts with oxygen and forms sulfur dioxide (SO2), which is present in flue gas generated by the combustion. Sulfur dioxide is a known pollutant. Accordingly, several countries have established environmental regulations to limit the amount of sulfur dioxide in flue gas. One method of reducing or eliminating sulfur dioxide in flue gas is to treat the flue gas in a desulfurization absorber tower. The flue gas can react with a slurry of wet limestone (CaCO3) in the absorber tower to form calcium sulfite (CaSO3) and calcium sulfate (CaSO4).
The absorber towers are typically 50-60 foot diameter pressure vessels accommodating limestone/gypsum slurry levels of 40 feet or more. The absorber towers generally define an inlet duct for introducing the flue gas into the absorber tower and an outlet duct for discharging treated gases. In some instances, an induced draft fan is positioned just ahead of the absorber tower in the inlet duct. Automatic controls are used to maintain predetermined slurry levels in the absorber tower.
Chemical reactions between the flue gas, the slurry and other chemicals in the absorber tower and air, which is injected into the slurry at the bottom of the absorber tower, can produce foam and aerated slurry floating on the slurry. If undetected, the foam and/or aerated slurry can accumulate and overflow into the inlet duct and damage the induced draft fan.